Move the emission of strict enum range metadata behind a flag (the same

flag as GCC uses: -fstrict-enums). There is a *lot* of code making
unwarranted assumptions about the underlying type of enums, and it
doesn't seem entirely reasonable to eagerly break all of it.

Much more importantly, the current state of affairs is *very* good at
optimizing based upon this information, which causes failures that are
very distant from the actual enum. Before we push for enabling this by
default, I think we need to implement -fcatch-undefined-behavior support
for instrumenting and trapping whenever we store or load a value outside
of the range. That way we can track down the misbehaving code very
quickly.

I discussed this with Rafael, and currently the only important cases he
is aware of are the bool range-based optimizations which are staying
hard enabled. We've not seen any issue with those either, and they are
much more important for performance.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153550 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Driver/CC1Options.td

@@ -178,6 +178,9 @@ def ffunction_sections : Flag<"-ffunction-sections">,
   HelpText<"Place each function in its own section (ELF Only)">;
 def fdata_sections : Flag<"-fdata-sections">,
   HelpText<"Place each data in its own section (ELF Only)">;
+def fstrict_enums : Flag<"-fstrict-enums">,
+  HelpText<"Enable optimizations based on the strict definition of an enum's "
+           "value range.">;
 def ftrap_function_EQ : Joined<"-ftrap-function=">,
   HelpText<"Issue call to specified function rather than a trap instruction">;
 def funroll_loops : Flag<"-funroll-loops">,

include/clang/Driver/Options.td

@@ -444,6 +444,7 @@ def fno_show_source_location : Flag<"-fno-show-source-location">, Group<f_Group>
 def fno_spell_checking : Flag<"-fno-spell-checking">, Group<f_Group>;
 def fno_stack_protector : Flag<"-fno-stack-protector">, Group<f_Group>;
 def fno_strict_aliasing : Flag<"-fno-strict-aliasing">, Group<f_Group>;
+def fno_strict_enums : Flag<"-fno-strict-enums">, Group<f_Group>;
 def fno_strict_overflow : Flag<"-fno-strict-overflow">, Group<f_Group>;
 def fno_threadsafe_statics : Flag<"-fno-threadsafe-statics">, Group<f_Group>;
 def fno_use_cxa_atexit : Flag<"-fno-use-cxa-atexit">, Group<f_Group>;
@@ -515,6 +516,7 @@ def fsigned_char : Flag<"-fsigned-char">, Group<f_Group>;
 def fstack_protector_all : Flag<"-fstack-protector-all">, Group<f_Group>;
 def fstack_protector : Flag<"-fstack-protector">, Group<f_Group>;
 def fstrict_aliasing : Flag<"-fstrict-aliasing">, Group<f_Group>;
+def fstrict_enums : Flag<"-fstrict-enums">, Group<f_Group>;
 def fstrict_overflow : Flag<"-fstrict-overflow">, Group<f_Group>;
 def fsyntax_only : Flag<"-fsyntax-only">, Flags<[DriverOption]>;
 def ftabstop_EQ : Joined<"-ftabstop=">, Group<f_Group>;

include/clang/Frontend/CodeGenOptions.h

@@ -94,6 +94,7 @@ public:
   unsigned SaveTempLabels    : 1; /// Save temporary labels.
   unsigned SimplifyLibCalls  : 1; /// Set when -fbuiltin is enabled.
   unsigned SoftFloat         : 1; /// -soft-float.
+  unsigned StrictEnums       : 1; /// Optimize based on strict enum definition.
   unsigned TimePasses        : 1; /// Set when -ftime-report is enabled.
   unsigned UnitAtATime       : 1; /// Unused. For mirroring GCC optimization
                                   /// selection.
@@ -205,6 +206,7 @@ public:
     SaveTempLabels = 0;
     SimplifyLibCalls = 1;
     SoftFloat = 0;
+    StrictEnums = 0;
     TimePasses = 0;
     UnitAtATime = 1;
     UnrollLoops = 0;

lib/CodeGen/CGExpr.cpp

@@ -872,8 +872,9 @@ static bool hasBooleanRepresentation(QualType Ty) {
 
 llvm::MDNode *CodeGenFunction::getRangeForLoadFromType(QualType Ty) {
   const EnumType *ET = Ty->getAs<EnumType>();
-  bool IsRegularCPlusPlusEnum = getLangOpts().CPlusPlus && ET &&
-    !ET->getDecl()->isFixed();
+  bool IsRegularCPlusPlusEnum = (getLangOpts().CPlusPlus && ET &&
+                                 CGM.getCodeGenOpts().StrictEnums &&
+                                 !ET->getDecl()->isFixed());
   bool IsBool = hasBooleanRepresentation(Ty);
   llvm::Type *LTy;
   if (!IsBool && !IsRegularCPlusPlusEnum)

lib/Driver/Tools.cpp

@@ -1487,6 +1487,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                     options::OPT_fno_strict_aliasing,
                     getToolChain().IsStrictAliasingDefault()))
     CmdArgs.push_back("-relaxed-aliasing");
+  if (Args.hasFlag(options::OPT_fstrict_enums, options::OPT_fno_strict_enums,
+                   false))
+    CmdArgs.push_back("-fstrict-enums");
   if (!Args.hasFlag(options::OPT_foptimize_sibling_calls,
                     options::OPT_fno_optimize_sibling_calls))
     CmdArgs.push_back("-mdisable-tail-calls");

lib/Frontend/CompilerInvocation.cpp

@@ -286,6 +286,8 @@ static void CodeGenOptsToArgs(const CodeGenOptions &Opts, ToArgsList &Res) {
     Res.push_back("-fno-dwarf-directory-asm");
   if (Opts.SoftFloat)
     Res.push_back("-msoft-float");
+  if (Opts.StrictEnums)
+    Res.push_back("-fstrict-enums");
   if (Opts.UnwindTables)
     Res.push_back("-munwind-tables");
   if (Opts.RelocationModel != "pic")
@@ -1135,6 +1137,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.NoDwarf2CFIAsm = Args.hasArg(OPT_fno_dwarf2_cfi_asm);
   Opts.NoDwarfDirectoryAsm = Args.hasArg(OPT_fno_dwarf_directory_asm);
   Opts.SoftFloat = Args.hasArg(OPT_msoft_float);
+  Opts.StrictEnums = Args.hasArg(OPT_fstrict_enums);
   Opts.UnsafeFPMath = Args.hasArg(OPT_menable_unsafe_fp_math) ||
                       Args.hasArg(OPT_cl_unsafe_math_optimizations) ||
                       Args.hasArg(OPT_cl_fast_relaxed_math);

test/CodeGenCXX/pr12251.cpp

@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 %s -emit-llvm -O1 -relaxed-aliasing -std=c++11 -o - | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -O1 -relaxed-aliasing -fstrict-enums -std=c++11 -o - | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -O1 -relaxed-aliasing -std=c++11 -o - | FileCheck --check-prefix=NO-STRICT-ENUMS %s
 
 bool f(bool *x) {
   return *x;
@@ -6,6 +7,12 @@ bool f(bool *x) {
 // CHECK: define zeroext i1 @_Z1fPb
 // CHECK: load i8* %{{.*}}, align 1, !range !0
 
+// Only enum-tests follow. Ensure that after the bool test, no further range
+// metadata shows up when strict enums are disabled.
+// NO-STRICT-ENUMS: define zeroext i1 @_Z1fPb
+// NO-STRICT-ENUMS: load i8* %{{.*}}, align 1, !range !0
+// NO-STRICT-ENUMS-NOT: !range
+
 enum e1 { };
 e1 g1(e1 *x) {
   return *x;